Purinergic (P2X) receptors are ATP-gated cation-selective channels. Each receptor is made up of three protein subunits or monomers. To date seven separate genes encoding P2X monomers have been identified: P2X1, P2X2, P2X3, P2X4, P2X5, P2X6, P2X7.
P2X7 receptors are of particular interest as the expression of these receptors is understood to be limited to cells having potential to undergo programmed cell death, such as thymocytes, dendritic cells, lymphocytes, macrophages and monocytes. There is some expression of P2X7 receptors in normal homeostasis, such as on erythrocytes.
Interestingly, a P2X7 receptor containing one or more monomers having a cis isomerisation at Pro210 (SEQ ID NO: 1) and which is devoid of ATP binding function has been found on cells that are understood to be unable to undergo programmed cell death, such as preneoplastic cells and neoplastic cells. This isoform of the receptor has been referred to as a “non functional” receptor.
Antibodies generated from immunisation with a peptide including Pro210 in cis bind to non functional P2X7 receptors. However, they do not bind to P2X7 receptors capable of binding ATP. Accordingly, these antibodies are useful for selectively detecting many forms of carcinoma and haemopoietic cancers and to treatment of some of these conditions.
WO02/057306A1 and WO03/020762A1 both discuss a probe for distinguishing between functional P2X7 receptors and non functional P2X7 receptors in the form of a monoclonal antibody.
To date it has been very difficult to obtain a hybridoma that generates useful amounts of antiserum against non functional P2X7 receptors, and in particular, antiserum that can be used in a range of diagnostic and therapeutic applications. Indeed, apart from the hybridomas and antibodies forming part of this invention, the Applicant is unaware of any other hybridomas or monoclonal antibodies against anti-non functional P2X7 receptors that could be robustly used in applications to detect or treat cancer and other conditions associated with non functional P2X7 receptor expression.